This invention relates broadly to radiation imaging devices which permit the direct recording of the distribution of radioactive material from a radiating source, such as a human organ. The invention is directed particularly to a novel gamma-ray camera and to several components used in such camera.
Visualization of isotope distribution within the living body has created important medical diagnostic procedures during the last decade. The two instruments which dominate the field of radioisotope imaging are the rectilinear scanner and the gamma-ray camera. The gamma camera, now being used to visualize nearly all organs that can be seen by conventional radioisotope scanners, has proved superior to these instruments in many ways in the field of basic research and clinical diagnosis and research.
Although the scanners can yield good picture definition, they are useless for studies of isotopes in motion (dynamic studies), for which exposures as little as 1 sec. may be derived to capture the changing distribution. The static camera, which has no moving parts and whose scintillation crystal must therefore be of large diameter so as to view the whole organ, appears to offer the only immediate solution. However, the static camera still remains equally useful for stationary distributions.
Attempts have been made to build a static camera around an image-intensifier as early as 1950, but such attempts were abandoned because prohibitively large isotope doses were needed to mask the fogging effects of intensifier tube noise on the picture. Several workers then turned to cameras using a multiplicity of photomultipliers to view the phosphor. Two instruments of this type are in current use, but their picture definition is limited. In one camera, at least, the maximum count rate is not really high enough for the dynamic studies.
The image-intensifier solution has been a continuous source of fascination, and designs have been proposed or built by a number of others. They all possess shortcomings, such as complex electronic systems, resulting in a large cost, and the necessity of continuous adjustments by a trained technician. Other disadvantages of prior devices are the long time interval required to obtain the radiation distribution data; the inability to obtain temporal information about the radiation distribution; the limitation on resolution made by the converting system and the collimator; and the limitation on the energy of the isotope used.